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To HVAC or Not HVAC

I am buying my first home. The current AC(old) has humongous air ducts in basement. My gas furnace is in the basement as well. I want to utilize basement space for kids but air ducts are in the way. I thought maybe if I get rid of the air ducts and add a new HVAC in the attic I could remove the basement ducts and redo the room. My closing date is approching in a few weeks. I want any work done before we move in.
Question:
1. How much(ballpark) would a HVAC small duct system cost for a 2100sf split level home.2. Will a attic HVAC system utilize a gas furnace in another area of the house or will I have to buy the heating attachment for the hvac?
3 Which is more cost efficient a gas furnace or a electric heating unit on a HVAC?
4. Can a HVAC Heating unit warm the whole house efficiently?

First, no pricing questions allowed. Only the HVAC contractor that see youor house can asnwer what it will cost.

Yes, you can have a cooling heating system installed in an attic.
It won't be as efficient as in the basement.
It will be hard to heat the basement with teh system installed in the attic. Unless you zone it. Or install another heat source for the basement in the basement.

I can't give you any pricing, somebody up north would have a better guess (we are in south central Texas), but to answer your other questions, yes you can put it in the attic if there is room and the attic area connects to all parts of the house (probably not in a split level). You can combine the gas system with a small air conditioning evaporator coil and condenser.

Some things you have options on, some things you don't. You can't change the Btu needs of the home. They are what they are based on the area, insulation, windows, air leak rate, etc. You can't therefore change the size of the furnace or the AC system and the size of the duct system installed is dependent on the size of the heating/cooling needs. Where you have the system installed is a choice you can make but you should be aware of some things first.

1. Warmer air rises, colder air falls (as compared to ambient)
2. Residential blowers do not have the "push" that commercial blowers do
3. A heating system installed in the basement and blowing up is working in concert with the laws of physics, warm air rises, while the AC system in the basement is working against the laws of physics. So the warm air system works better from below (in the basement) while the AC system would work better from above (in the attic).

I can only tell you what our company policy/preference is based on experience. When we're using a single system to both heat and cool a home of 1 story in height, the system can be either in the attic or the basement and total comfort can be achieved if all work is done "by the books".

When using a single system to both heat and cool a home of two stories, it's generally preferrable to have the system in the basement for more even heating in the winter (approx. 9-months in NJ) and will probably suffer from some slight temp differences between the 1st and 2nd floor in the summer during the day. In some instances, we've been able to put the furnace or air handler on the first floor (or second floor if there's also a 3rd floor involved) and run the ducts along the first floor ceiling/second story floor joists so that it's possible to heat the lower floor(s) from the ceilings and the upper floor(s) from the floors. IMO, any residential system trying to push the air up or down 2 full floors will suffer some temperature variations in one of the two seasons, again, due to the laws of physics. Once you know these things, you can decide which compromise you're willing to make to accommodate your situation. If you do make a change, please be sure you hire a company that's truly professional, does heat gain/loss calculations (Manual 'J') and duct layout/sizing per Manual 'D'. If they don't do those calculations, don't hire them. Period.

If YOU want change, YOU have to first change.

If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!